The fertility rate in Flint, Michigan, dropped precipitously after the city decided to switch to lead-poisoned Flint River water in 2014, according to a new working paper.

That decline was primarily driven by what the authors call a “culling of the least healthy fetuses” resulting in a “horrifyingly large” increase in fetal deaths and miscarriages. The paper estimates that among the babies conceived from November 2013 through March 2015, “between 198 and 276 more children would have been born had Flint not enacted the switch in water,” write health economists Daniel Grossman of West Virginia University and David Slusky of Kansas University.

In April 2014, Flint decided to draw its public water supply from the Flint River, a temporary measure intended to save costs while the city worked on a permanent pipeline project to Lake Huron. Residents immediately began complaining about the odor and appearance of the water, but well into 2015 the city was still assuring residents that the water was safe to drink.

Subsequent testing by Flint authorities and outside agencies turned up lead levels that in some cases were dozens or hundreds times higher than the Environmental Protection Agency’s safety threshold. A September 2015 study showed that the proportion of Flint children with high lead levels in their blood had roughly doubled after the water change. The city finally switched back to Lake Huron water in October 2015.

The harmful effects of lead exposure on children’s health are well-documented. They include cognitive deficiencies, increased antisocial behavior, lower educational attainment, and a host of problems affecting the brain, kidneys and liver.

Less well-known are lead’s effects on fetal health. Literature reviewed by Grossman and Slusky shows that maternal lead exposure is linked to “fetal death, prenatal growth abnormalities, reduced gestational period, and reduced birth weight.” A 2013 study, for instance, found an increase in fetal deaths and a reduction of births in Washington, D.C., from 2000 to 2003, when lead levels were elevated in the city’s drinking water.

Grossman and Slusky wanted to know if something similar happened in Flint after lead-poisoned water was introduced in 2014. They compared birth and fetal death rates in Flint with those in other Michigan cities, including Lansing, Grand Rapids, Dearborn and Detroit.

“These areas provide a natural control group for Flint in that they are economically similar areas and, with the exception of the change in water supply, followed similar trends in fertility and birth outcomes over this time period,” the authors say.

What they found was “a substantial decrease in fertility rates in Flint for births conceived around October 2013, which persisted through the end of 2015. Flint switched its water source in April 2014, meaning these births would have been exposed to this new water for a substantial period in utero (i.e., at least one trimester).”

Other cities in Michigan showed no such drop.

During this time period, residents in Flint were generally unaware of the amount of lead in their water. “Because the higher lead content of the new water supply was unknown at the time, this decrease in (the general fertility rate) is likely a reflection of an increase in fetal deaths and miscarriages and not a behavior change in sexual behavior related to conception like contraceptive use,” Grossman and Slusky conclude.

They next turned to deaths of fetuses of 20 weeks gestation and older, excluding abortions, which are reported by hospitals. They found that “fetal death rates increased in Flint but did not change substantially in other areas following the water change.” The change in Flint amounted to a 58 percent increase in fetal deaths, relative to areas not afflicted by lead-poisoned water, a change the authors characterized as “horrifyingly large.”

The authors say their number probably undercounts the total number of miscarriages and fetal deaths for several reasons: “(1) They do not include abortions; (2) they do not include miscarriages that occur before 20 weeks of gestation; and (3) they are restricted to hospitals reporting these events,” Grossman and Slusky said.

The paper’s findings on fertility and fetal death rates largely mirror the effects observed in Washington from 2000 to 2003. And the authors note that many effects probably fall outside the scope of the current research: The children born during this period were subsequently exposed to lead outside of the womb as well, potentially setting themselves up for a host of physical and behavioral problems later in life.

Flint is currently working on overhauling its water infrastructure, a process that local authorities say is likely to take years. At the end of 2016, 10 percent of Flint homes still had lead concentrations of 12 parts per billion or higher in their water, three times the level observed in Detroit.

Although the EPA threshold for safe drinking water is 15 parts of lead per billion, according to the World Health Organization “there is no known level of lead exposure that is considered safe.”

Flint, according to 2016 Census estimates, is 53 percent African-American. In addition, 45 percent of Flint’s residents live in poverty, and census data released last week showed that it is the nation’s poorest city.